Aneroid barometer



Jan. 9, 1945. I. E. M CABE ANEROID BAROMETER 2 Sheets-Sheet 1 Filed June 24, 1942 K Y O E ma W W 0 N w I A M E m Y B a Q Jan. 9, 1945. E. M CABE'.

ANEROID BAROMETER Filed June 24, 1942 2 Sheets-Sheet 2 INVENTOR. IRA f. M 'CABE ATTORNEY.

Patented Jan. 9, 1945 UNITED STATES PATENT, OFFICE 1,367,034

Applicatio: 31:21:82.4, 448,315

This invention relates to improvements in aneroid barometers and similar diaphragm actuated instruments such as radiosondes sent aloft by balloons for making recordings of atmosphericconditions at various altitudes and more particularly to means to compensate for the effect of temperature changes upon these diaphragms and thereby eliminate errors in recording pressure changes.

The actuating member of an aneroid barometer may take the form of a Bourdon tube or two similar spac'ed apart thin metal discs having similar concentric corrugations secured to each other about their peripheries to provide a cylindrical metal box, and the air exhausted. Each corrugated thin disc is made of metal so elastic that it readily yields to alterations in atmospheric pressure. At sea. level the corrugated discs or diaphragms are compressed or forced toward each other by the high atmospheric pressure thereby increasing the stress in the diaphragm material.

sation would be one in which the degree of comh pensation decreases commensurately with the decrease in effect of temperature changes upon the diaphragm at higher altitudes until the stress is relieved in the diaphragm material.

It is an object of this invention to provide a simple form of compensating means for the effect of temperature changes in the diaphragm of aneroid barometers in which the compensation becomes less as the diaphragm expands under the decreasing pressure as the altitude increases to such an extent that temperature compensation is substantially zero at extremely high altitudes where temperature changes have little or no effect upon the diaphragm material to cause expansion or contraction of the diaphragm.

With this and other objects in view, reference is made to the accompanying sheets of drawings At sea level, therefore, with the material un- In instruments of this character when designedor intended for use only at sea level or at fixed altitudes, compensation for the effect of temper-' ature changes of the diaphragm are included so that recordings of the atmospheric pressure will not be affected thereby.

However, where the instrument is to be sent aloft in airplanes or as a part of radiosonde devices carried by balloons to altitudes of 40,000 to 60,000 feet, the forms of temperature compensation employed in devices which are intended for use at fixed altitudes no longer obtain.

Since the stress in the diaphragm material Y diminishes as the atmospheric pressures diminish at higher altitudes, the effect of temperature changes in the diaphragm material is likewise reduced as higher altitudes are reached and there is less need for temperature compensation to secure accurate pressure recordings indicating those altitudes.

The desirable-means of temperature compen which illustrate preferred forms of this invention with the understanding that minor changes may be made without departing from the scope thereof.

In. the drawings:

Figure 1 is a fragmentary view in elevation illustrating this invention as applied to a dual aneroid diaphragm construction forming a part of a radiosonde, balloon ascension meteorological instrument for actuating a movable contact over asound-track by means of whichthe altitude attained by the instrument through its ascent and descent may be radioed to the earth.

Figure 2 is a top plane view in detail of the indicator arm and compensating device.

Figure 3 is a view partly in end elevation and section of Figure 2 looking toward the right.

Figure 4 is a similar view illustrating the temperature compensating diaphragm arrangement of Figure 1 as applied to a calibrated indicating barometer.

Figure 5 is an enlarged detail view of this invention illustrating the compensating correction made for a temperature drop at sea level.

Figure 6 is a view similar to Figure 5 illustrating the effect upon the compensating means as higher altitudes are reached.

In the embodiment of this invention in a radiosonde instrument as illustrated in Figure 1,two aneroid diaphragms I and 2 are superimposed upon each other in fixed relation with the lower disc of the upper diaphragm centrally secured to the upper disc of the lower diaphragm and with the lower disc of the lower diaphragm centrally secured to an adjustable stud 3 mounted in the lower bracket 4 of the instrument. The upper bracket 5 of the instrument supports the upper end of the indicator or contact arm 8 upon a pivot I mounted between spaced apart depending plates 8. The free end of the indicator arm 6 is mounted to travel over a sound track 9 adjustably carried between the ends of the brackets l and 5, as shown in Figure 1. The arm 8 is intended to provide an electric circuit connection through a series of electrical contact bars forming the sound track to a radio transmitting device included in the radiosonde instrument.

As shown in Figure 2, it is preferable to pivotally mount the indicator arm 8 upon the longer arm II) of a U-shaped bracket II mounted for rotation about the pivot I and the free end of the indicator arm 6 is normally held in contact with the sound track 9 by a coil spring I2, as shown. The shorter arm I3 of the U-shaped bracket II mounts a plate I upon its exterior surface having an elongated slot I5 allowing th plate to be slideably adjusted over the pivot I and secured in the desired position by a set screw IS. The upper portion of this plate is provided with a guiding flange II extending over the upper surface 01' the arm I3 and an inturned guiding flange I8 adapted to travel over the lower side of the arm I3, which guiding flange is provided with an angular extension I9 depending at an angle therefrom and terminating in an angular foot 20. A strip 2| of bi-metallic metal is secured at its lower end to the foot and supports at its upper end a connecting pin 22 upon the side most adjacent the pivot I. A vertical plate 23 is secured upon a diameter of the upper diaphragm I and is provided over the center of the diaphragm with a connecting pin 24 which mounts one end of a connecting link 25, the other end of which is mounted upon the connecting pin 22 carried upon the free end of the bi-metallic strip 2I so that movement of thediaphragms I and 2 in expanding and contracting is transmitted through the connecting link 25 to the indicator arm 6. A coil spring 26 with one end anchored in the plate 23 upon the diaphragm I and the other in the end of the shorter arm I3 of the U-shaped bracket iI normally urges the free end of the indicator arm 6 towards the bottom of the sound track 9.

In the construction just described, at sea level, the diaphragms I and 2 will be collapsed. Adjustment of the diaphragms through the proper adjustment of the stud 3, the plate I4 and track 9 to position the free end of the indicator arm 6 at the lower end of the sound track is contemplated to provide means for calibrating the indicator to the sound track 9. As the atmospheric pressure changes, the expansion or contraction of the diaphragms will cause the indicator to move and register the pressure causing such changes.

Th manner in which the sheet of temperature changes upon the diaphragms are compensated is shown in an exaggerated manner upon the enlarged detail views of Figures 5 and 6. In Figure 5, the position of the parts at the pressure and temperature for which the instrument has been calibrated is shown in full lines with the center of the connecting pin 22 indicated by A. Upon a decline in temperature with no change in atmospheric pressure and without any compensating means, the diaphragm would expand and the center of the connecting pin 22 would be moved to the position indicated by A through the connecting link 25 causing the indicator arm 6 to assume the position shown in dotted lines.

pensating means to an The strip 2| of bimetallic metal is deformed by a drop in temperature, as shown in dot and dash lines, to cause its free end to move in the direction or the pivot I and move the center of the connecting pin 22 to the position indicated by A, whereby no movement about the pivot I is imparted to the indicator arm 8, as the distance between the original position of the center of th connecting pin 22 and the position assumed at A is along the longitudinal center line of the carrier 'arm' III to correspond to the upward movement of the connecting pin 24 in moving from the normal position of the diaphragm I to the expanded position shown in dotted lines.

The position of the elements when the instrument is subjected to the lower pressures of higher altitudes is shown in full lines in Figure 6 where the external and internal pressures upon the dia phragms reach a point of equilibrium and the diaphragm material is relieved of the stresses encountered when differentials in exterior and interior pressures are encountered at sea level or low altitudes. Therefore, the effect of temperature variations upon the diaphragms does not cause a change in the state of the diaphragm material to impart movement to the diaphragm and compensation for such changes in temperature is not needed. As shown in Figure 6, a rise in temperature causing the free end of the bi-metal- 110 member 2I to move to the position shown in dot and dash lines will move the center A of the connecting pin 22 to the position A along the longitudinal center line of the carrying member Ill without imparting any movement to the free end of the indicator 6 to affect the pressure recordings.

Figure 4 illustrates the application of this comindicating aneroid barometer in which the lower end of the carrying member ID is expanded to form a toothed quadrant 21 to engage a pinion 28 mounting the indicator 29 so that, with the other parts being of the same construction as hereinbefore described, the effects of temperature changes at different altitudes upon the instrument will be compensated.

In an instrument constructed in accordance with this disclosure, the error in pressure recordings clue to temperature changes is reduced to a minimum over the entire scale of the instrument, the degree of temperature compensation being maximum at sea 'level and diminishing to zero at extremely high altitudes. It is thereby understood that the principle of this invention may be applied in various ways as long as it substantially secures the results attained in the manner shown by the use of bimetallic strips.

What I claim is:

1. In a pressure indicating device, a pivoted indicating arm, an aneroid diaphragm made of material having a positive temperature coefficient of expansion, means imparting movement of the diaphragm to the arm including a bracket upon the arm, a floating pivot, a link pivotally connected to the diaphragm and to said pivot, a thermal strip having one end secured to the bracket with its free end mounting the floating pivot, said thermal strip being mounted on the bracket in of atmospheric pressure the movement of the indicator arm through the bracket and thermal strip moves the strip toward a position whereby the strip moves the pivot at right angles to the lines of force exerted upon it by the diaphragm through the link so that the strip is substantially non-compensating upon changes in temperature.

2. The structure of claim 1 wherein th floating pivot is adapted for movement by the thermal strip substantially along the longitudinal center line of the arm.-

3. In a pressure indicating device, a pivoted indicating arm, an aneroid diaphragm made of material having a positive temperature coefficient of expansion, means for imparting movement of the diaphragm to the arm including a floating pivot, a link connection from the diaphragm to said pivot, a thermal strip connecting said pivot to the arm, said strip movable with the arm to vary its position with respect to said link to provide a movement of the pivot compensating for movement imparted thereto by the diaphragm upon temperature changes at high atmospheric pressures, the relationship of the strip and link varying upon movement of the arm due to lowering atmospheric pressures causing movement of the pivot by said strip upon temperature changes to lessen the compensating efiect.

4. The structure of claim 3 wherein the floating pivot is mounted for movement along the longitudinal center line of the arm.

5. In a pressure indicating device, a pivoted indicating arm, an aneroid diaphragm made of material having a positive temperature coeflicient of expansion, means for imparting movement of the diaphragm to the arm including a link pivoted at one end to the diaphragm, a bracket upon CERTIF-I GATE the arm, a strip of thermal metal having a pivot movable along the longitudinal center line of the arm and providing a connection for the free end of the link, said strip being so secured to the bracket that the relation of the strip and link at high atmospheric pressures provides a directional movement of the pivot compensating for movement of the diaphragm upon changes in temperature, the relation of the strip and link changing with the movement of the arm to vary the directional movement of the pivot with respect to the movement imparted thereto by the diaphragm to reduce the degree of temperature compensation with lowering atmospheric pressures.

6. In a pressure indicating device, a pivoted indicating arm, an aneroid diaphragm made of material having a positive temperature coefiicient of expansion, means for imparting movement of the diaphragm to the armincluding a link connection with the diaphragm and a thermal strip having a pivoted connection with the link, said strip adapted for movement with the indicating arm to vary the directional movement of the piv- 0t upon temperature changes between the high and low atmospheric pressures to which the diaphragm is responsive, the movement of the pivot in relation to the direction of movement imparted to the link by the diaphragm compensating for temperature changes at high atmospheric pressures and non-compensating at low atmospheric pressures.

7. The structure of claim 6 wherein the pivot is mounted for movement along the longitudinal center line of the arm.

IRA E. McCABE.

or CORRECTION.

January 9, 1915.

IRA E McCABE It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, line 28, for the word "contradiction" read -contraction--;

and

that the said Letters Patent should beread with this correction therein that thesame may conform to the record of the case in the Patent Office.

Signed and sealed this 10th day of April, A. D. 1914.5.

(Seal) Leslie Frazer Acting Commissioner of Patents. 

